Synthesis of tricyclic beta-lactams related to cephalosporins

Several compounds related to the cephalosporin antibiotics and containing a novel tricyclic beta -lactam system have been prepared in the expectation that they might have a more strained beta -lactam ring than the parent comp ounds. In the event, synthetic problems required that the compounds prepare d containing this system had a reduced thiazine ring. The ring strain was n ot exceptional as judged by the absorption frequencies in the infra red.